The present invention relates in general to compositions, methods and apparatuses for flushing paints or other coatings from equipment such as automated and manual paint sprayers and paint dip installations, and in particular to a new and useful solution which is water-based and uses low amounts of volatile organic compound (VOC) solvents, which have conventionally been used in much greater concentrations for flushing paints and other coatings, in particular, non-water-based paints and other coatings.
U.S. Pat. Nos. 5,701,922 and 5,632,822 are both incorporated here for reference.
It is known to purge automated paint sprayers and paint dip equipment during maintenance and color changes using solvents based on:
______________________________________ Alcohol Fluorinated Hydrocarbon Terpene Aliphatic Hydrocarbon Chlorinated solvent Aromatic Hydrocarbon ______________________________________
All of these solvents are considered hazardous and most forms are considered to be volatile organic compounds or VOC's. They may be used in the 100% pure form or as blends, using combinations of the solvents.
VOC's are heavily regulated by the Environmental Protection Agency (EPA) and by SARA and HAPS laws. The EPA regulates the amount of VOC which any particular company can emit into the atmosphere. This ceiling limits the production output of the company which, in particular, when automated equipment is used, it is much less than the total output that the company may be capable of sustaining without such regulations. The ceiling is particularly difficult to deal with also because these companies use paints which themselves contain high percentages of VOC solvents. The solvent percentages range from 5% to 80%, depending on the paint.
Current paints and other coatings fall into six categories as follows:
______________________________________ Epoxy Polyester Polyurethane Polyamid Enamels Water Borne ______________________________________
For the purpose of this disclosure, paints will be grouped into the general category referred to as coatings, which may include not only paints but other liquids meant to be coated onto surfaces. Coatings, in turn, are divided generally into VOC coatings containing some VOC solvents and non-VOC coatings, such as water-borne coatings.
Various automated and manual devices, equipment and techniques are known for applying coatings onto structures. Among these is the use of electrostatic spraying equipment which pumps paint from a holding vessel or drum and sprays the paint through a manual air gun or automated, robot controlled, reciprocating paint nozzle, disc or bell-shaped applicator. The paint may also be pumped to a dip tank which applies the coating by dipping structures into the tank. For electrostatic coating, the paint is charged with 20,000 to 80,000 volts and applied to a grounded structure or substrate to be coated. The advantage to electrostatics is that it allows most of the coating to go directly onto the substrate and minimizes over-spraying and excess air emissions.
The use of electrostatic spraying thus reduces VOC discharge and permits high-volume application of coatings while still remaining within the strict EPA regulations. This technique also reduces the amount of paint used during the operation.
When a new color is needed for the substrates, all paint lines containing the last color must be purged. Currently this is done by drawing solvent from a holding vessel or drum and circulating it through the system lines and out through the sprayers or drains. Some of the solvent may be recirculated while a remainder of the solvent is disposed of as a hazardous waste. A new color is then introduced into the system. Problems associated with these types of solvents, whether they are VOC or not, include flammability, toxic fume exposure to employees, evaporative losses and odors.
One example of an electrostatic nozzle and other equipment particularly suited for robot-controlled coating, is manufactured by Binks Manufacturing Company of Franklin Park, Ill. One such nozzle supplied by Binks is known as the Mini-Mizer series, which is a high-speed circumferencial atomizer, especially suited for atomizing high-solids coatings, water-borne coatings and conventional solvent base coating systems.
Due to the presence of high voltage, a serious problem which occurs, in particular, during the purging operation, is the problem of arcing. Both the nozzles and the hoses and lines connected to the nozzles can pick up charges and pose an arcing hazard. Although conductive materials can be sprayed with the Mini-Mizer nozzle, the manufacturer of the nozzle advises users to utilize an extra degree of electrical insulation from ground, for the spray equipment.
One company which is involved in the spraying of substrates and which must comply with EPA regulations concerning emissions, is Lozier, which operates from seven different locations and which utilizes robotic spray booths. It is estimated that a company like Lozier would utilize approximately 4,000 gallons of cleanser per month for its seven locations for exclusive use in purging the spray equipment. It is common to require on the order of 40 color changes per day, switching colors among approximately 180 available colors. Each color change must be followed by a purge cycle which is as quick and effective as possible to permit quick restarting of the spraying equipment with a new color.
Reducing VOC's and other undesirable components from the purging fluid, would represent a substantial improvement in the field, resulting in increased production rates which are still within the EPA requirements.
Currently, acetone is not considered a VOC. Although many manufacturing facilities are using acetone to reduce their VOC emissions, there are some severe setbacks when using this alternative:
1. Acetone is highly flammable;
2. Acetone has severe overexposure precautions as it pertains to the user; and
3. Acetone by itself is ineffective and, therefore, is mixed with other solvents which are typically HAPS, VOC, flammable, and SARA regulated.
Typical formulations include:
30% Acetone 70% MEK (HAPS, SARA, Flammable)
40% Acetone 60% Xytene (HAPS, SARA, Flammable)
50% Acetone 50% Toluene (HAPS, SARA, Flammable)
These solvents still emit high levels of VOC (50-70%) and these blends are not water reducible, compared to the low VOC, low vapor pressure aqueous blends of the present invention which emit 6-15% VOC. The present invention is a dramatic improvement environmentally and produces a friendlier atmosphere for in-plant operation than acetone based solvents.
The present invention is also more closely tailored to use in purging equipment containing heat curable liquids, although other liquids can also be purged with the composition of the present invention.